【作者】 杨剑；

【导师】 钱壮志； 易发成；

【作者基本信息】 长安大学 ， 构造地质学， 2009， 博士

【摘要】 中国南方早寒武世广泛分布富有机质的黑色岩系，是PGE、Au、Ag、Ni、Mo、V等的重要载体，常产出Ni-Mo-PGE矿床、V-Cu-U矿床、磷矿床和重晶石矿床等大型-超大型金属和非金属矿床。黑色岩系也是沉积岩中的一种烃源岩，与化石能源有直接关系。黑色岩系的研究已成为当今地学界的热点研究领域之一，具有重要的理论意义和经济价值。黔北是下寒武统黑色岩系发育的典型地区，前人已在古生物学、地层学、地球化学和矿床学方面进行了大量研究工作，但全面系统的有机地球化学和元素地球化学的结合研究尚不多见。本文通过研究黔北地区黑色岩系的矿物岩石学特征、有机地球化学特征和元素地球化学特征，在查明黑色岩系物质组成的基础上，探讨了黑色岩系形成环境、元素来源、赋存状态和富集规律。本文通过野外露头观察、室内岩矿分析，结合前人研究资料，确定了研究区下寒武统黑色岩系的岩性序列自下而上划分为5个岩性段，即黑色硅岩（下硅质层）、磷块岩（磷矿层）、多元素富集层（镍矿层和钼矿层）、黑色条纹状碳泥质硅质岩（上硅质层）、黑色碳质伊利石页岩。为了查明黑色岩系的矿物组合特征，对各类岩石样品进行了X射线粉末衍射分析和扫描电镜分析。下寒武统牛蹄塘组黑色岩系主要由粉砂岩、页岩、石煤、硅岩、碳酸盐岩、磷块岩、重晶石岩等组成，主要矿物组合为石英、伊利石、绿泥石、磷灰石、黄铁矿、重晶石和方解石等，其中镍-钼多元素富集层中硫化物矿物主要有黄铁矿、闪锌矿、毒砂、辉钼矿、针镍矿、砷镍矿、辉砷镍矿、辉铜矿、黄铜矿和方铅矿等。基于研究区的大地构造、岩石地层和古生物特征，确认黔北遵义地区黑色岩系形成的岩相古地理环境为近滨-远滨相，即浅水陆架区，向东逐渐转变为斜坡-盆地区，即深水陆棚区。深大断裂构造成为含矿物质来源的构造通道，海底火山喷溢和侵入活动提供大量的成矿物质和“热源”。在综合分析前人研究成果的基础上，认定早寒武世及其以前，研究区发育一系列深大断裂并长期活动，沿深大断裂发生较强的海底火山喷溢和侵入活动，控制了区域地质构造的发展和矿产的分布，对黑色岩系中多元素的富集起着重要作用。测定岩样有机碳和有机硫含量，目的是为了查明黑色岩系的有机质丰度。黑色岩系有机碳含量平均为5．481％，最高达9．29％，有机硫含量平均为4．532％，最高达23．30％，富含有机碳和有机硫。黑色岩系中有机质主要来源于藻类和菌类生物。有机硫，连同黄铁矿，指示一种封闭-半封闭的缺氧还原环境。有机质成熟度是有机质热演化程度的反映。黑色岩系氯仿沥青“A”族组分中，具有高饱和烃、低芳烃和高非烃的族组分分布特征，表现出以富含类脂化合物和蛋白质为特点的低等水生生物来源的腐泥型有机质的特点。黑色岩系干酪根显微组分绝大部分为腐泥组，干酪根类型为Ⅰ型（腐泥型），此类型干酪根与细菌和藻类有关。有机碳含量和镜质体反射率证实，黑色岩系是较好的烃源岩，有机质成熟度高，达到生油门限或高成熟（交替作用）阶段。通过饱和烃气相色谱分析，检测出生物标志化合物，从分子级水平探讨地质体中有机分子化合物的演化规律。黑色岩系高主峰碳、较小的∑nC₂₁^-／∑nC₂₂⁺值和(nC₂₁+nC₂₂)／(nC₂₈+nC₂₉)值，可能与成岩后期作用有关。黑色岩系OEP为1．04～1．12，奇偶优势比接近于1，无奇偶优势或具有微弱的奇偶优势，表明低等海洋浮游生物是有机质的主要来源。黑色岩系Pr／Ph值为0．80～1．18，小于1或近于1，显示出还原或弱还原沉积环境。黑色岩系各岩样碳同位素组成的差别意味着沉积时古海洋环境的变化。黑色岩系δ¹³C_PDB值为-23．74‰～-31．63‰之间，总体属于L型无定形干酪根，且更富轻碳同位素(¹²C)。剖面上从磷块岩→镍矿层→钼矿层，δ¹³C值逐渐减小，海平面处于上升阶段，缺氧还原环境逐渐增强，在钼矿层δ¹³C值减小到最低值，代表了最大海进期，之后在黑色页岩δ¹³C值增大，海平面有所下降，缺氧还原强度减弱。热演化温度是成岩成矿的重要因素。黑色岩系样品的固体沥青反射率测定结果为5．25％～6．27％，折算出来的镜质体反射率为3．645％～4．455％，得到黑色岩系的受热温度为92℃～250℃。按照干酪根和微体藻类化石颜色指标，大致确定该地层的古地温为60℃～110℃。结合前人黄铁矿热电系数法测温（100℃～240℃）和包裹体均一法测温（226℃～230℃和113℃～153℃），判定牛蹄塘组黑色岩系的受热温度介于60℃～250℃之间，经历的最高古地温估计为200℃～250℃，属中、低温沉积成岩成矿作用，并以低温（200℃以下）沉积成岩成矿作用为主。为了探明黑色岩系中贵金属元素的来源，系统测定了样品Au、Ag、PGE含量。结果表明，铂族元素（包括Au和Ag）在黑色岩系多金属元素富集层，特别是钼矿层中得到富集。从贵金属元素的含量、特征参数、配分模式来判定，黑色岩系不具有地外物质的性质，铂族元素（包括Au和Ag）不是来源于地外，而是来自沿着深大断裂上涌的海底岩浆喷溢，元素的异常富集是海底含矿热卤水与正常海水共同作用的结果。稀土元素总量（∑REE）在多金属元素富集层之钼矿层中出现峰值，达315．12×10^-6。La／Sm均大于1，代表地幔热柱或异常型，暗示黑色岩系形成时有地下深部物质介入。REE球粒陨石标准化分布模式为曲线右倾斜，LREE富集型。δEu=0．52～0．87＜1，δCe=0．68～0．88＜1，Eu、Ce均呈负异常，表明黑色岩系形成于缺氧的还原沉积环境。REE北美页岩标准化模式显示出Ce负异常，LREE＜HREE，北美页岩组合样标准化曲线近于水平，反映了海相热水沉积特征。黑色岩系多金属元素富集层也是其他微量元素（如Mo、Se、As、Sb、Tl、Ni、U、Pb、Bi、Cu、Cs、Zn、V等）的富集体。微量元素总量在钼矿层达到最高(110759．11×10^-6)。δU＞1，表现为缺氧沉积环境。微量元素富集系数高，U／Th＞1，表明受到较强的热液活动的影响。岩石中微量元素赋存特征是沉积物形成环境和成岩变化的综合反映。黑色岩系富含有机质，粘土矿物成分高，Ni-Mo矿层以硫化物矿物为主，表明元素赋存状态主要为硫化物态、有机质结合态和粘土矿物吸附态等。根据上述研究，结合前人成果，简要阐述了PGE、REE、Ni、Mo、Au、Ag、V、U、Cu、Pb、Zn、As、Sb、Tl、Se等元素在黑色岩系中的赋存状态。在全面分析有机地球化学特征和元素地球化学特征的基础上，结合地质构造背景，探讨了黑色岩系的形成环境和多金属元素富集规律：在542Ma左右的寒武纪早期，黔北地区发育古热液喷口，沿深大断裂发生多期次海底火山喷溢和侵入活动，深部热源物质上涌，与地表水、地下水和海水一道形成具一定温度的热卤水，进行热水循环或热水活动。热卤水在流动过程中，大量溶解元古代武陵期基性-超基性岩物质中的有用元素，进一步形成含矿热卤水，这种含矿热卤水是黑色岩系多金属元素的直接来源。在滞留、还原的台缘斜坡带（水深200m左右），表层水中繁衍着大量的藻类和浮游生物，生物生产力高，大量生物死亡下沉，向海底提供充分的有机物质，遗体腐烂分解吸收大量溶解氧，造成大洋中层水体缺氧还原环境，致使形成的黑色岩系富含有机质，有机质在多金属元素的迁移聚集过程中发挥着重要作用。研究区早寒武世缺氧事件（环境）可与全球大洋缺氧事件对比。多金属元素矿化经历了沉积期、成岩期、后生期和表生期各个阶段。矿化温度以低温（200℃以下）为主。黑色岩系沉积以来，铂族元素（包括Au和Ag）在低温条件下进行了重新分配（成岩期）、迁移与富集（后生期）。表生期只在地表不深处有一定作用。黑色岩系形成环境和地球化学的研究，为查明黑色岩系的成因、构建多金属元素的富集模式、探索黑色岩系型矿床的成矿机理奠定了基础，以促进黑色岩系型矿床，特别是铂族元素矿床的找矿工作。更多还原

【Abstract】 As is known to us, there are many series of black rock scattered in the south of China, which are theimportant carriers of PGE, Ag, Au, Ni, Mo, V etc., and often generate large-scale or super-large-scale metaland non-metal deposits, such as Ni-Mo-PGE deposit, V-Cu-U deposit, phosphorus deposit, barite depositetc. Black shale series is also one of hydrocarbon source rocks of sedimentary rocks and closely related tofossil energy. Research on the black shale series has become a hot area in geology, which is of significancein theory and economy. Northern Guizhou is the typical region where the Lower Cambrian black shaleseries developed, wherealot of research has been done by many geologists through the methods ofpaleontology, stratigraphy, geochemistry and metallogeny while the research through combining organicgeochemistry with elemental geochemistry is not frequently used. In light of petromineralogy, organicgeochemistry and elemental geochemistry features of the black shale series in this area, on the basis of thecomposition of the black shale series, this paper mainly discusses on the formation environment, source ofelements, mode of occurrence and enrichment rules.Through field observation, rock-mineral analysis interior the lab and referring to the former studies,it proposes that the lithological sequences of the Lower Cambrian black shale series can be divided intosuch 5 layers from the bottom to the top as black quartzite （lower silicalite）, phosphate （phosphorite）,metal-rich shale （Ni ore bed and Mo ore bed）, black striation ampelitic-argillaceous silicalite （uppersilicalite）, and black ampelitic ledikite shale.In order to get the features of the composition of the black shale series, we used X-ray powderdiffraction and SEM-EDAX analysis. Black shale series of Niutitang formation of lower Cambrian ismainly composed of siltite, shale, stone-like coal, quartzite, carbonatite, phosphorite, baritic rock etc, andthe main mineral assemblage contains quartz, ledikite, chlorite, phosphorite, pyrite, barite, calcite etc, andsulfide minerals in Ni-Mu multielement enrichment layer mainly include pyrite, sphalerite, arsenopyrite,molybdenite, millerite, placodine, dobschauite, chalcocite, chalcopyrite and galenite etc.According to tectonic background, lithostratigraphic and paleontological characteristics, it is affirmedthat lithofacies paleogeography of the black shale series occured in Zunyi area of Guizhou province is anearshore-offshore facies, which means a shallow-water continental shelf, from where towards east itevolved gradually into a slope-basin area, which means a deep-water continental shelf:Deep fault become the channel of mineral matter and hot bittern seawater sediments as well as magmatic intrusion can provide the mineral matter and“Hot Resource”. On the basis of the research data,we believe that at lower Cambrian and before, a series of deep fault grows in the investigated region withsome long-term activities, along which strong volcano eruption and magmatic intrusion occurred,controlling the development of regional geological tectonic and the distribution of minerals, which playedthe key role in the multi-element enrichment of the black shale series.Tests of the contents of organic carbon and organic sulfur of rock samples are made to find out theorganic abundance of the black shale series. The average content of organic carbon and organic sulfur is5.481% and 4.532%, the highest content up to 9.29% and 23.30%, respectively. The organic of the blackshale series takes their origin from algae and fungi biology. The organic sulfur and pyrite indicate aclosed-semi closed anoxic and reducing environment.The degree of organic maturation of black shale series can reflect its degree of thermal evolution.The component of chloroform bitumen“A”has the distribution of high saturated hydrocarbon, lowaromatic hydrocarbon and high nonhydrocarbon, that characterized in sapropelic organic matters evolvedfrom lower hydrobiont which are rich in lipids and proteins. The kerogen macerals of the black shale seriesare mostly formed by sapropel, and the kerogen belongs to the type“Ⅰ”（sapropel type）, closely related tofungi and algae. Confirmed by what the organic carbon content and vitrinite reflectance indicated, the blackshale belonged to comparatively good hydrocarbon source rocks, with a high maturity of organic matters,reaching to the stage of oil-generative threshold and high maturity （or alternating action）.Biomarker compounds are detected on the analysis of the gas-facies chromatogram of saturatedhydrocarbon, according to which we can discuss the evolvement of organic molecule compounds ingeologic bodies at the molecule level. The black shale series has an evidently high value of main peakcarbon and lower∑nC₂₁^-/∑nC₂₂⁺ and (nC₂₁+nC₂₂)/(nC₂₈+nC₂₉) ratios, which is possibly related to theeffect of late diagenesis.In the black shale series, OEP is 1.04～1.12, approximate tol at the odd evenpredominance, having no （or little） odd even predominance. It indicates that the organic matters weremainly from lower oceanic planktons. Additionally, the Pr/Ph ratio （0.80～1.18） of the black shale seriesless than or approximate to 1, reflects a weak reducing sedimentary environment.The differences of the C-isotopic composition in all kinds rock samples were regarded as the changeof the environment when paleo-ocean sediment started.δ¹³C_PDB ratio of the black shale [0]series isbetween -23.74‰and -31.63‰. It generally belongs to the type“L”amorphous kerogen and is richer inlight C-isotope. In section, from phosphate, Ni ore bed to Mo ore bed, theδ¹³C value decreases gradually, which indicates that the sea level lies in rising period and anoxic and reducing environment graduallyincreased, theδ¹³C value of Mo ore bed decreases to the minimum, representing a maximum transgressionperiod; and later, the increasingδ¹³C value of the black shale denotes a degressive sea level, companyingwith a decreasing anoxic and reducing environment.[0]The temperature of thermal evolution of black shale series is of a great significance in expoundingrock-forming and ore-forming condition. The solid bitumen reflectance data of the black shale seriessamples is between 5.25% and 6.27%, vitrinite reflectance data between 3.645% and 4.455%, converted bythe experience formulas, and the heated temperature of black shale series between 92℃and 250℃.According to the color index of kerogen and micro-algae fossil, it is demonstrated that thepaleotemperature of the black shale series ranges from 60℃to 110℃. By combining with pyritethermoelectricity coefficient thermometry result （100℃～240℃） and inclusion equal thermometry result（226℃～230℃and 113℃～153℃） it shows that the heated temperature of the black shale series ofNiutitang formation is between 60℃and 250℃, and the max paleotemperature between 200℃and 250℃,which belongs to the middle-lower temperature sedimentary and rock-forming and ore-forming actions inLower Cambrian black shale series in northern Guizhou.The content of Au, Ag, PGE were tested for making clear of the source of these elements in the blackshale series. Platinum-group elements （including Au and Ag） is enriched in the metal-rich shale, especiallyin Mo ore bed of the black shale series. The PGE abundance, elements’ interrelation, relative parametersand PGE patterns indicated that PGE sourced from hot bittern seawater sediments from magma, and highenrichments of PGE resulted from mixing of hot bittern seawater sediments and normal seawatersediments.The total REE content of the black shale series reaches its peak value (up to 315.12×10^-6) in Mo orebed of metal-rich shales, La/Sm＞1, representing mantle plume or abnormally style, which suggests thatmantle matters have been joined while forming the black shale series. The chondrite-normalized REEpattern is a right curve tilting of LREE enrichment.δEu andδCe range from 0.52 to 0.87 and from 0.68 to0.88, respectively, all of which is less than 1, and the negative anomaly of Eu and Ce showed that the blackshale series were deposited in an anoxic sea environment. The North America shale-normalized REEpattern shows negative anomaly of Ce, LREE＜HREE, which is nearly smooth, reflecting the characteristicof marine hydrothermal sediments. The enrichment layer of the multi-metal elements is the enrichment body of other trace-elements,such as Mo、Se、As、Sb、Tl、Ni、U、Pb、Bi、Cu、Cs、Zn、V etc. That the total content of the trace-elementsreaches the highest value (110759.11×10^-6) in Mo ore bed. The data that has been got,δU＞1, suggests areducing sedimentary environment. The high enrichment coefficient of trace-elements and the data that hasbeen got, U/Th＞1, indicate that they might be affected by comparatively strong hydrothermal activities.The enrichment characteristic of the trace-elements in rocks can integratively reflect the formationenvironment of sediments and rock-forming process. The black shale seires is rich in organic matters andclay minerals, mainly with the sulfide in Ni-Mo ore bed, which indicates that the occurrences of theelements are represented as the results of sulfide, organic matter bound and clay mineral adsorption. Basedon the research above and combining with the former research, this paper is to simply discuss theoccurrence of elements in black shale series, including PGE、REE、Ni、Mo、Au、Ag、V、U、Cu、Pb、Zn、As、Sb、Tl、Se etc.On the basis of organic geochemistry, elementary geochemistry and geologic structure background,this paper discusses the formation environment of black shale series and the enrichment rule of multi-metalelements. At earlier Cambrian of about 542Ma, when the north of Kuizhou province generated thepaleohydrothermal vents and -multiple submarine volcano eruption and magmatic intrusion occurred alongdeep fault, it caused deep“hot resource”upwelling, together with surface water, ground water and seawater, because of which the hot bittern seawater at certain temperature came into being, resulting in hotwater recycling or hot water activity. And in the process of flowing, the hot bittern seawater dissolved lotsof useful elements of the basic-ultrabasic rocks at Proterozoic Wuling period, that furthered the formationof the ore-bearing hot bittern seawater, which is the direct source of the multi-metal of the black shaleseries. On the belt of the resident and reducing platform margin slope （about 200m deep of water）, a lot ofalgaes and planktonthes had been bred in surface layer water, and the biologies had a high reproducingability and provided with adequate organic matters for the seabed as they died and began to sink, whosedecaying and dispersed reliquiaes absorbed a great number of dissolved oxygen, resulting in an anoxic andreducing environment of water body of middle ocean and then the formation of black shale series, in whichthe organic matters is enriched, acting greatly on the movement and gathering of multi-metal elements.Therefore, comparison can be made between the anoxic event （or environment） of Earlier Cambrian of thisarea and that of global oceans. The mineralization of multi-metal elements had experienced several periodsof sedimentary stage, diagenesis stage, epigenetic stage and hypergene stage. The mineralization characterized in low temperature （below 200℃）. Ever since the black shale series had begun in sediment, aperiod of reassembly （which represents diagenesis stage） and movement and enrichment （which indicatesepigenetic stage） had been put on platinum-group element （including Au and Ag） at the low temperature.The effect of the epigenetic stage had been posed only on places of certain depth next to the earth surface.Study on the formation environment and geochemistry of the black shale series can establish thefoundation for the genesis of the black shale series, enrichment model of multi-metal element anddiscussing mineral-generative mechanism of black shale series deposit and promote exploration of theblack shale series deposits, especially the platinum-group element deposit.更多还原